I'm sorry if my knowledge of the AV world is causing me to ask a silly question, but I've spent literally a dozen hours searching, and have come up with nothing.

I work in a school for kids with autism, and the teachers frequently record a class session for evaluation, allowing them to individualize each child's curriculum. The video feeds are multiplexed analog signals sent over coax. For years this was recorded as needed using VCRs.

What we'd really like to do is replace all of the VCRs with some type of DVR the provides equivalent usage. Ideally a teacher would go to one of the TV's, pop in an SD card, start/stop recording, and walk off with their video on their portable media (just like they did with a VHS tape).

Does anything like this even exist? A DVR that uses removable (non-optical) media the way a VCR used tapes?